Javadoc

Returns an id for use as the
ClientBehavior source. ClientBehavior implementations that submit back
to the Faces lifecycle are required to identify which component
triggered the ClientBehavior-initiated request via the
javax.faces.source request parameter. In
most cases, th source id can be trivially derived from the element
to which the behavior's client-side script is attached - ie. the
source id is typically the id of this element. However, in components
which produce more complex content, the behavior script may not be able to
determine the correct id to use for the javax.faces.source
value. The
ClientBehaviorContext#getSourceId method allows the component
to pass this information into the
ClientBehavior#getScriptimplementation.